1. Field of the Invention
The present invention relates to a process for the viscosification of an organic liquid which includes the steps of forming two solvent systems one of an organic liquid or oil and the other of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent systems, a viscosity of both solvent systems being less than about 1,000 cps; dissolving an anionic polymer such as neutralized sulfonated elastomeric polymer (water insoluble) in the solvent systems of the organic liquid and polar cosolvent to form a first solution, and dissolving an unsulfonated elastomeric polymer using the same polymeric backbone as the sulfonated polymer in the organic liquid to form a second solution, a concentration of the neutralized sulfonated polymer in the first solution being about 0.2 to about 10 weight percent, a concentration of the unsulfonated elastomeric polymer in the second solution being about 0.2 to about 10 weight percent, the viscosity of both solutions being less than about 2,000 cps; mixing both solutions together to form a solution of an interpolymer network of sulfonated elastomeric polymer and copolymer, and admixing or contacting said solution of said sulfonated elastomeric polymer and said unsulfonated elastomeric polymer with about a 5 to about 500 volume percent water, the water being immiscible with the organic liquid and the polar cosolvent transferring from the organic liquid to the water phase, thereby causing the polymer containing phase to gel (i.e. thicken).
2. Description of the Prior Art
There are many applications for very viscous or gelled solutions which are quite diverse. There are also a number of physical and chemical techniques for preparing such systems. The present invention is concerned with a process for gelling a fluid system by contacting the fluid system with a relatively low viscosity, organic liquid solution of interpenitrating polymers. The potential applications for this process and the products derived therefrom will be evident in the instant application. Some of these applications are as a viscosifier for hydrocarbon solutions, such as a shut-off technique in oil well applications and a spacer or soluble plug in oil well applications.
The instant invention differs from a number of applications, Ser. Nos. 223,482; 136,837; and 106,027, filed by Robert Lundberg et al, one of the instant inventors. These previously filed applications were directed to the gelling of the organic liquid by a water insoluble, neutralized sulfonated polymer whereas the instant invention is directed to the gelling of an organic fluid by a mixture of a sulfonated polymer and unsulfonated polymer.
In the current invention, two polymers are mixed to produce an interpolymer network which at relatively low concentration forms a three-dimensional network with a gel-like behavior. The blends of an associating and a non-associating polymer are much more effective in forming a network than are single associating polymers leading to gels of higher strength.
Controlled gelation is achieved by dissolving the two polymers in the presence of a cosolvent which can ultimately be removed causing instantaneous gelation. The cosolvent acts to prevent efficient formation of a three-dimensional network and hence helps in reducing solution viscosity. However, as soon as the cosolvent is removed, a network is formed. In this way, the polymer solution containing a cosolvent can be transported or pumped into a region where gelation is desired, and the cosolvent will be removed at that region.
The instant invention describes a process which permits (1) the preparation of polymer solutions of the sulfonated polymer and unsulfonated polymer in organic liquid having reasonably low viscosities (i.e., less than about 200 cps); and (2) the preparation of extremely viscous solutions or gels of the organic fluid from such solutions by a process of mixing or contacting water with the polymer solution. These operations are achieved by the use of the appropriate concentration: about 0.2 to 10.0 weight percent of water insoluble, sulfonated and unsulfonated polymers.
In the instant process, the role of the polar cosolvent is that of solvating the ionic groups while the main body of the solvent interacts with the polymer backbone. For example, xylene is an excellent solvent for the polystyrene backbone and when combined with 5 percent methanol will dissolve, readily and rapidly, the previous example of lightly sulfonated polystyrene.
The remarkable and surprising discovery of the instant invention is that when small (or large) amounts of water are combined and mixed with solutions of ionic polymers dissolved at low concentrations (about 0.2 to 10 weight percent) in such mixed solvent systems as those described above, a phase transfer of the cosolvent occurs from the nonpolar organic liquid phase to the water phase, thus by causing the polymer containing phase to gel (i.e. thicken). Indeed, it is possible to achieve increases in viscosity of the polymer solution by factors of 10.sup.3 (1,000) or more by the addition of only 5 to 15 percent water based on the polymer solution volume. This unusual behavior is postulated to arise from the removal of the polar cosolvent from the organic liquid phase into the separate aqueous phase.
In the instant invention, the interpolymer network in hydrocarbon solution is obtained by mixing two polymers which will strongly enhance the relaxation times of the system. One polymer contains anionic groups along or pendant to its backbone which may be either partially or fully neutralized and thus is an associating polymer. The other could be the precursor polymer from which the associating polymer is made of, or any other polymer whose molecular architecture is nearly the same as the backbone of the associating polymer. The former criterion is desired, since it assures the dissolution of the polymers without macroscopic phase separation. In solution the caging effects of the non-associating polymer chains around and along the associating sites of the associating polymer chains is believed to lead to strong network formation.
A polar cosolvent added to the polymer blend solution interferes with network formation and thus reduces the viscosity or gel characteristics of the solution.
A solution of such a polymer blend system in the presence of a cosolvent will have a relatively low viscosity. Gelation of this solution will be affected by removing the cosolvent. Such removal can be obtained by selective extraction, evaporation of a volatile cosolvent, chemical reaction, precipitation, absorption, or any other method that would shift the balance from the state of interaction the polymer functional group to another preferred state.
A simple means for extraction of a polar cosolvent is the addition of water or a second polar fluid to the solution. If the second fluid is not miscible with the primary solvent, an extraction will take place into the second phase. The new equilibrium will be a function of the volume of each phase as well as temperature and pressure conditions. Equilibrium can be further shifted by adding an adsorbing or reacting species to the extracting phase.